The present invention relates generally to the fields of chemistry, chemical engineering, process and environmental monitoring, food industry and medicine. More particularly, the present invention is directed to electrodes for determination of the presence of peroxides, as well as methods for the preparation and use thereof.
There is a growing need for sensitive, selective and accurate measurement of hydrogen peroxide, organic (hydro)peroxides and lipid hydroperoxides in clinical, pharmaceutical, food and industrial processes and environmental applications. For example, the development of flavin enzyme-based assays or electrodes require sensitive measurement of H.sub.2 O.sub.2 formed in enzyme catalyzed reactions Guilbault, G. G. & Lubarano, G. J., Anal. Chim. Acta 1973, 64, 439-455!. H.sub.2 O.sub.2 determination is also important to ensure the safety and quality of pharmaceutical and cosmetic formulations Wang, J. et al., Analyst 1993, 118, 277-280!. Measurement of lipid hydroperoxides, the primary products of lipid peroxidation, is of great medical significance in connection with cancer development, aging processes and other pathological conditions Mannino, S. et al., Anal. Lett. 1994, 27, 299-308; Eun, J. -B. et al., J. Food Sci. 1994, 59, 251-255; Shantha, N. C. & Decker, E. A., J. AOAC International 1994, 77, 421-424; Roozen, J. P. & Linssen, J. P. H., In Lipid Oxidation in Food. ACS Symposium Series 500, St. Angelo, A. J., Ed., American Chemical Society: Washington, D.C., 1992, Chapter 17 & 18, pp. 302-321; Hageman, G. et al., Lipids 1989, 24, 899-902!. Monitoring of organic (hydro)peroxides formed during the reaction of ozone with organic compounds in the atmosphere and drinking water or directly released into the environment from numerous industrial processes is desirable because of their adverse health effects IARC Monographs on the Evalution of the Carcinogenic Risk of Chemicals to Humans. Allyl Compounds, Aldehydes, Epoxides and Peroxides, IARC: Lyon, France, 1985, Vol. 36, pp. 267-321; Glaze, W. H., Environ. Sci. Technol. 1987, 21, 224-230; Kok, G. L. et al., Environ. Sci. Technol. 1978, 12, 1072-1076!.
Conventionally titrimetric Bassett, J. et al., In Textbook of Quantitative Inorganic Analysis, Vogel, A. I., Ed., 4th edition, Longman: London, 1978, p. 355!, spectrophotometric Sellers, R. M., Analyst 1980, 105, 950-954!, colorimetric Ito, Y. et al., Assoc. Off. Anal. Chem. 1981, 64, 1448-1452!, chemiluminescent Kok, G. L. et al., Environ. Sci. Technol. 1978, 12, 1072-1076! and amperometric methods are used for the detection and measurement of peroxides. Because of the very low detection limits, amperometry is the most widely used technique Yamada, K. et al., Lipids 1987, 22, 125-128!. Amperometric determinations of peroxides are generally performed by oxidation at +0.6 to +0.7 V vs. Ag/AgCl on a platinum electrode (for H.sub.2 O.sub.2) Guilbault & Lubarano (1973), supra! or reduction at -0.3 to -1.0 V vs. Ag/AgCl on gold/mercury amalgam or glassy carbon electrode (for organic and lipid hydroperoxides) Cosgrove, M. et al., Analyst 1988, 113, 1811-1815; Funk, M. O. et al., Anal. Chem. 1980, 52, 773-774!. At such large overpotentials, substances such as ascorbic acid, uric acid and acetaminophen interfere under oxidation conditions, while oxygen and compounds such as benzoquinone, nitrobenzene, etc., interfere at reduction potentials. Low selectivity is therefore a major limitation in amperometric determinations.
To overcome the limitations imposed by the requirement of large overpotentials on the selectivity of these sensors, different approaches have been proposed. Platinized and rhodinised carbon electrodes have been developed to lower the oxidation potential for H.sub.2 O.sub.2 to +0.4 V White, S. F. et al., Electroanalysis 1994, 6, 625-632!. Although the oxidation potential for H.sub.2 O.sub.2 on such electrodes is lowered, detection is still not completely free of interference Hajizadeh, K. et al., Anal. Chim. Acta 1991, 243, 23-32!. Determination of H.sub.2 O.sub.2 by reduction at electrodes modified with Ru(NH.sub.3).sub.6.sup.3+ -incorporated montmorillonite clay Oyama, N. & Anson, F. C., J.Electroanal.Chem. 1986, 199, 467-470!, palladium/iridium Cox, J. A. & Jaworski, R. K., Anal. Chem. 1989, 61, 2176-2178! and iron phthalocyanine Qi, X. & Baldwin, R. P., Electroanalysis 1993, 5, 547-554! have been reported. These electrodes, however, have limitations. The determination of H.sub.2 O.sub.2 at the Pd/Ir modified electrode is performed at -0.3 V (vs. Ag/AgCl) at which dissolved oxygen is also reduced and therefore interferes. Reductions of H.sub.2 O.sub.2 at Ru(NH.sub.3).sub.6.sup.3+ -incorporated montmorillonite clay and iron phthalocyanine modified electrodes require strongly acidic environment (pH 2) and therefore limit the application of these electrodes for construction of flavin enzyme-based biosensors. Iron phthalocyanine modified electrodes have also been used to detect organic (hydro)peroxides at lower reduction potential Qi, X. & Baldwin, R. P., supra!.
Use of enzyme (peroxidase) modified electrodes to determine H.sub.2 O.sub.2, organic (hydro)peroxides and lipid hydroperoxides by reduction have been reported. These enzyme modified electrodes, operating between 0 and -0.2 V vs. Ag/AgCl, are reported to be free of interference from ascorbate, urate and paracetamol Mannino et al. (1994), supra; Cosgrove et al. (1988), supra Kulys, J. J. et al., Bioelectrochem. Bioenerg. 1981, 8, 81-88; Wang, J. et al., Anal. Chim. Acta 1991, 254, 81-88; Vreeke, M. et al., Anal. Chem. 1992, 64, 3084-3090; Wollenberger, U. et al., Anal. Lett. 1990, 23, 1795-1808; Gorton, L. et al., Analyst 1992, 117, 1235-1241; Mori, H. et al., Anal. Lett. 1992, 25, 1643-1656. Nonetheless, the use of the heretofore known enzyme peroxidase electrodes also entails disadvantages, such as short shelf-life.
It is an object of the present invention to provide electrodes which do not suffer from all of the drawbacks of the prior art electrodes, as well as methods for the preparation and use thereof.